Hi Kathryn,

Yellowwood trees (Cladrastis kentukea) are indeed pretty especially this time of the year.  They are hardy in this area, but have a weak wood structure and are susceptible to storm damage. They also prefer full sun, at least 6-hrs/day.

Your tree could be leaning for a couple of reasons: it is seeking more sunlight, or it was damaged at sometime.

Young trees can be staked to prevent leaning, but correcting it once it happens is another matter.  

I suggest you have an arborist look at the tree and tell you what, if anything can be done.  You can find an arborist through Maryland Arborist Society: http://mdarborist.com. Click on the "Consumers" tab on the top right and it will give you a link for a list of licensed arborists in Maryland.

Good luck and thanks for contacting us,

Judy